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Tuesday, 3 April 2012

Configuring vSphere 4.1 VM to Host DRS Affinity Rules

Configuring vSphere 4.1 VM to Host DRS Affinity Rules

Introduction

VMWare vSphere’s DRS (Distributed Resource Scheduler) is
mainly used for load balancing virtual machines (VMs) on a cluster. While most
virtualization admins will want to run DRS in fully automated mode - i.e.,
vSphere decides on its own which VM is assigned to which ESX Server - there may
be certain instances when you would want to enforce some conditions by setting
what are known as DRS Affinity Rules.

Instances wherein you would want to enforce DRS Affinity Rules

So what are some of those instances wherein you would want to dictate which
VM or VMs should (or should not) be assigned to a particular ESX Server or group
of ESX Servers?Licensing IssuesSome applications running on your VMs
may have licensing peculiarities such as:

Those that require the application to be run on only one CPU; a restriction
that can have complications if you have a single-CPU server along with a bunch
of dual-CPU servers.

Those that restrict the application to one specific server with a specific
serial number.

Availability RequirementsYou might want to prevent a
group of VMs from running on particular ESX servers.Performance RequirementsYou might want to assign some
VMs to your newly acquired multiple-CPU server.

How to configure VM to Host DRS Affinity Rules

Let’s now proceed to see how you can keep a single VM or a group of VMs to
either a single ESX server or a group of ESX servers.
Open your vSphere Client and find the cluster on which the rules will be
enforced.
In the screenshot below, we’ll be enforcing the rules on DRS Cluster 1, which
contains four ESX servers and a bunch of virtual machines.
Right-click on the cluster in question and, in the corresponding context
menu, select Edit Settings.
First, we’ll create a Virtual Machines DRS Group and assign virtual machines
to it.
To do that, go to the left-hand-side panel and select DRS Groups
Manager. Next, go to the Virtual Machines DRS Groups
panel and click that panel’s Add button.
You can now select VMs that you’d like to add to your VM group.
Click the “>>” button to add the selected VMs to the VM group. Once
you’re done, give your group a name (e.g. vCenter-VM-Group), then click the
OK button.
Back at the DRS Groups Manager, you can then create a Host
DRS Group. This is the host DRS group where you’ll be assigning your newly
created virtual machines DRS group.

Go to the Host DRS Groups panel and click the corresponding Add
button.
You’ll then see a similar window as the one where you added VMs to a group
(see two screenshots back). Just like what you did with the VMs, select hosts
that you want to add to the host DRS group and click the “>>” button.
Note: Assigning the VM group to a host group is optional. It is possible to
assign your VM group to a single host or ESX server.
Now, give the host group a name (e.g. ESX-DR-Group-1) and click the
OK button.
So now you have both a Virtual Machines DRS Group and a Host DRS Group.
Notice that the screenshot below shows the DRS Groups Manager
tab. This is also exactly what you’ll see if you select the DRS Groups
Manager in the left-hand-side panel.

Create DRS Affinity Rule

You are finally ready to create your DRS Affinity Rule. Click the
Rule tab and come up with a name for your rule (e.g.
Pin-vCenter-VMs-to-ESX-Group-1).
Now, for the following drop-down lists, select the following items:

Type = Virtual Machines to Hosts

Cluster VM Group = the Virtual Machines DRS Group you
created (e.g. vCenter-VM-Group)

Cluster Host Group = the Host DRS Group you created (e.g.
ESX-DR-Group-1). This is where the VM group is supposed to run.

Notice that we skipped one drop-down list. In the screenshot, it’s the one
that says “Must run on hosts in group”. That drop-down list is where
you’re supposed to select the actual rule that will apply to the VM group-host
group pair.
Expand that list, select the rule you wish to implement, and click
OK.
That should create your VM to Host DRS Affinity Rule.
You’ll see something like this (see screenshot below) in the succeeding
window. You’ll have to click the “+” symbol to expand the VM to Host Rule and
reveal the corresponding Cluster VM Group and Cluster Host Group on which the
rule will apply.
That’s it. You have just created a vSphere 4.1 VM to Host DRS
Affinity Rule.